High-temperature aquifer thermal energy storage systems for storage and utilization of excess heat are a promising element for decarbonization strategies of district heating systems. Based on a combination of literature review and expert consultation, this study aims to identify potential environmental and economic key factors determining a sustainable integration of high-temperature aquifer thermal energy storage systems into district heating networks. For this objective, we use several methods in five steps to narrow down the potentially high number of influencing factors. We identify hard boundary constraints for project development, the most relevant life cycle phases and related internal factors. Moreover, we identify influencing external factors and methodological factors that impact environmental and economic outcomes from a systemic perspective. Our findings suggest that potential key factors mainly pertain to the construction and operation phases, which are significantly affected by drilling, heat production, and the electricity required for submersible pumps and heat pumps for injection and extraction of stored heat. Identifying these factors enhances the comprehension and transparency of decision support based on life cycle assessment and life cycle costing. The results further guides research and practical improvement actions towards the most pertinent factors.

Highlights • Five steps approach to identify potential environmental-economic key factors. • Key factors relate to life cycle phases “Construction” and “Operation”. • Energy demand and subsurface construction are crucial internal factors. • Political and knowledge-related factors influence environmental-economic results. • Methodological key factors relate to system boundaries and temporal aspects.